Liquid filled vibration isolator

ABSTRACT

A liquid filled vibration isolator incorporates an inner cylindrical metal member  10 , an intermediate metal member  20  coaxially disposed on the outside of the inner cylindrical metal member and at a position apart from the inner cylindrical metal member, having paired ring portions  21  at two ends in the axial direction and a connection portion  25  structured to integrally connect the ring portions  21  to each other and having an opening  26  formed in a direction in which main vibrations are input; and a rubber member  30  structured to connect the intermediate metal member and the inner cylindrical metal member  10  to each other and incorporating a recess  33  corresponding to the opening  26 . A passage forming member  40  for covering the opening  26  on the outer surface of the connection portion  25  has a circular-arc plate  41  extending in the circumferential direction, at least one partition wall  42  extending from either end of the circular-arc plate in the circumferential direction except for the two ends of the circular-arc plate in the widthwise direction and end walls  43  stood erect at two ends of the circular-arc plate in the circumferential direction so that a reciprocative passage groove  44  is formed. Moreover, an air discharge opening  47  which penetrates the partition wall  42  in the radial direction is provided for a portion of the partition wall.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a liquid filled vibration isolator for use in, for example, an engine mount of a car body.

[0002] Hitherto, a liquid filled vibration isolator of the foregoing type has a structure, for example, as shown in FIGS. 12 to 14. The liquid filled vibration isolator incorporates an inner cylindrical metal member 1 and a cylindrical intermediate metal member 2 disposed around the inner cylindrical metal member 1 and apart from the inner cylindrical metal member 1, the inner cylindrical metal member 1 and the intermediate metal member 2 being coaxially disposed. The intermediate metal member 2 has paired ring portions 2 a disposed at the two axial ends of the intermediate metal member 2 and a connecting portion 2 b for integrally connecting the ring portion 2 a to each other. The connecting portion 2 b has a cross section formed circular-arc-like shape, the cross section being a cross section in a direction perpendicular to the axis thereof. The diameter of the connection portion 2 b is smaller than that of each of the ring portion 2 a. The connection portion 2 b has one opening 2 c formed in a direction in which main vibrations are input. A cylindrical rubber member 3 incorporates paired side walls 3 a for connecting the two axial directional ends of the intermediate metal member 2 and the inner cylindrical metal member 1 to one another. Moreover, the rubber member 3 incorporates an arm portion 3 b extending between the side walls 3 a at a position on the inside of the connection portion 2 b in the axial direction. Thus, the arm portion 3 b connects the connection portion 2 b and the inner cylindrical metal member 1 to each other. The rubber member 3 has a thin diaphragm portion 3 c disposed on the outside of the connection portion 2 b such that a gap 3 d is created from the connection portion 2 b. The diaphragm portion 3 c extends to the two side portions in the axial direction of the liquid filled vibration isolator. In addition, the rubber member 3 has a recess 3 e surrounded by the paired side walls 3 a and the arm portion 3 b and opened in the opening 2 c. A passage forming member 4 is joined between the ring portions 2 a, the passage forming member 4 closing the opening 2 c in the connection portion and having a shape extending on the two sides in the circumferential direction.

[0003] As shown in FIGS. 15A to 15C, the passage forming member 4 incorporates a circular-arc plate 4 a having a width slightly larger than the opening 2 c. Moreover, a plurality of partition walls 4 b are disposed on the outside of the circular-arc plate 4 a at positions between the two sides (the two sides included) in the widthwise direction such that the distances among the partition walls 4 b are substantially the same and the partition walls 4 b are alternately extended from the two ends of the circumferential direction. Moreover, end walls 4 c are stood erect at the two ends of the circular-arc plate 4 a in the circumferential direction. Thus, a reciprocative passage 4 d which reciprocates between the two ends in the circumferential direction is formed. A communication opening 5 a allowed to communicate with the recess 3 e is formed at an end of the reciprocative passage 4 d. A communication opening 5 b allowed to communicate with the gap 3 d is formed at another end of the reciprocative passage 4 d. As shown in FIG. 13, a stopper 6 a made of rubber to have elasticity is molded on the reverse side of the passage forming member 4 by vulcanization. A resin stopper 6 b is disposed on the inside of the stopper 6 a.

[0004] An outer cylindrical metal member 7 incorporating a rubber seal 7 a on the inner surface thereof is coaxially disposed on the outside of the intermediate metal member 2, the outer cylindrical metal member 7 being secured to the intermediate metal member 2 by drawing. The outer cylindrical metal member 7 closes the space from the intermediate metal member 2 in a fluid-tight manner so that a main liquid chamber 8 a is formed in the recess 3 e. Moreover, a sub-liquid-chamber 8 b is formed in the gap 3 d. In addition, an orifice passage 8 c is formed in a space from the passage forming member 4, the orifice passage 8 c being formed to allow the main liquid chamber 8 a and the sub-liquid-chamber 8 b to communicate with each other.

[0005] The inner cylindrical metal member 1 of the foregoing liquid filled vibration isolator is connected to a support member (not shown) of the car body. Moreover, the outer cylindrical metal member 7 is connected to a support member (not shown) adjacent to the engine. The upper stopper 6 a and the lower stopper member 6 b are disposed in the vertical direction which is the direction in which the main vibrations of the engine are input. In addition, the main liquid chamber 8 a and the sub-liquid-chamber 8 b are disposed in the vertical direction across the inner cylindrical metal member 1. If vibrations are produced between the inner cylindrical metal member 1 and the outer cylindrical metal member 7, the elastic action of the rubber member and the resonant action of the liquid column by liquid which flows in the orifice passage 8 c damp the vibrations.

[0006] Since the passage forming member 4 of the liquid filled vibration isolator is made of metal, for example, an aluminum die-cast, there arises a problem in that the weight of the liquid filled vibration isolator is made heavier if the absolute length of the orifice passage is elongated. The passage forming member 4 joined to the intermediate metal member 2 is immersed in a liquid to fill the inside portion of the recess 3 e and the like with the liquid. Then, the outer cylindrical metal member 7 disposed on the outer surface of the intermediate metal member 2 is subjected to the drawing process in the liquid. Since only one opening (the communication opening) of the passage forming member 4 allowed to communicate with the recess 3 e is provided, air in the main liquid chamber 8 a cannot easily be discharged. Thus, a long time is required to complete the liquid filling operation. Another problem arises in that residual air in the main liquid chamber 8 a deteriorates the performance for isolating vibrations.

SUMMARY OF THE INVENTION

[0007] To overcome the foregoing problems, an object of the present invention is to provide a liquid filled vibration isolator which can easily and reliably be filled with liquid and which enables the weight of a passage forming member thereof to be reduced.

[0008] To achieve the foregoing object, according to one aspect of the present invention, there is provided a liquid filled vibration isolator comprising; an inner cylindrical metal member; a cylindrical intermediate metal member disposed on the outside of the inner cylindrical metal member at a position apart from the inner cylindrical metal member and incorporating paired ring portions formed at two ends in the axial direction, a connection portion for integrally connecting the paired ring portions to each other and an opening formed in a direction in which main vibrations are input; a rubber member constituted by paired side wall portions for connecting the paired ring portions of the intermediate metal member and the inner cylindrical metal member to each other, an arm portion for connecting the paired side wall portions in an axial direction to connect the connection portion and the inner cylindrical metal member, a recess surrounded by the paired side wall portions and the arm portion and opened in the opening, a thin diaphragm portion disposed opposite to the opening in a radial direction such that the thin diaphragm portion is disposed apart from the inner cylindrical metal member and the arm portion at a position between the paired ring portions of the intermediate metal member, and a rubber sealing portion disposed on the outer surface of the cylindrical intermediate metal member; a passage forming member incorporating a circular-arc plate disposed on the outside of the connection portion and extending in the circumferential direction to close the opening, a reciprocative passage groove formed in the outer surface of the circular arc plate to reciprocate between two ends in the circumferential direction, a first communicate opening allowed to communicate with the recess at one end of the reciprocative passage groove and a second communicate opening opened in the circumferential direction at another end of the reciprocative passage groove; and an outer cylindrical metal member secured to the outside portion of the cylindrical intermediate metal member and the passage forming member, arranged to cause the sealing portion to close a space from the cylindrical intermediate metal member in a liquid-tight manner to form a main liquid chamber in the recess and a sub-liquid-chamber defined by the diaphragm portion and capable of forming an orifice passage in a space from the passage forming member to allow the main liquid chamber and the sub-liquid chamber to communicate with each other, wherein the reciprocative passage groove which is formed into the orifice passage is formed by at least one partition wall extended from either end of the circular-arc plate in the circumferential direction except for the two ends of the circular-arc plate in the widthwise direction and end walls stood erect at two ends of the circular-arc plate in the circumferential direction. When a plurality of the partition walls are provided, the partition walls disposed at substantially the same distances in the widthwise direction are alternately extended from the two ends of the circular-arc plate in the circumferential direction except for the two ends of the circular-arc plate in the widthwise direction.

[0009] In the present invention structured as described above, no partition wall is disposed at the two ends of the passage forming member in the widthwise direction. But in the foregoing portion, a passage can be formed between the other partition wall on the inside in the widthwise direction and the inside portion of the ring portion of the cylindrical intermediate metal member in the axial direction. Therefore, a long passage having an appropriate width can be maintained. Therefore, the vibrations isolating function of the orifice passage of the liquid filled vibration isolator can be maintained. Moreover ,since no partition wall is disposed at the two ends in the axial direction, the weight and manufacturing cost of the passage forming member can be reduced.

[0010] An air discharging opening which penetrates the partition wall in the radial direction and allowed to communicate with the recess may be provided for a portion of the partition wall. Since the air discharging opening is formed in a portion of the partition wall of the passage forming member, removal of a bubble in the main liquid chamber can easily and reliably be performed through the air discharging opening when an operation for filling the recess with liquid is performed. Since the air discharging opening is provided for a portion of the partition wall, the width of the passage of the passage forming member is reduced in the foregoing portion. However, omission of the partition wall at the two ends of the passage forming member in the widthwise direction enables reduction in the width of the passage to be prevented.

[0011] A structure may be employed in which a projection outwards projecting in the radial direction is provided for a portion of the reciprocative passage groove, and an air discharging opening which penetrates the projection in the radial direction and allowed to communicate with the recess is provided for the projection. Since the air discharging opening is formed in the projection provided for a portion of the reciprocative passage of the passage forming member, removal of a bubble in the main liquid chamber can easily and reliably be performed through the air discharging opening when an operation for filling the recess with liquid is performed. Since the projection is provided for a portion of the reciprocative passage, the width of the passage of the passage forming member is reduced in the foregoing portion. However, omission of the partition wall at the two ends of the passage forming member in the widthwise direction enables reduction in the width of the passage to be prevented.

[0012] A passage forming recess allowed to communicate with the reciprocative passage groove may be provided for a portion of the cylindrical intermediate metal member opposite to the air discharging opening in the axial direction. Therefore, the air discharging opening provided for a portion of the partition wall or the projection causes the width of the passage of the passage forming member to be reduced. However the passage forming recess provided for the corresponding position of the cylindrical intermediate metal member enables the width of the reciprocative passage in the narrowed portion to relatively be enlarged.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a side view schematically showing a liquid filled vibration isolator according to an embodiment of the present invention;

[0014]FIG. 2 is a plan view showing a state of the liquid filled vibration isolator in which a portion of an outer cylindrical metal member has been removed;

[0015]FIG. 3 is a cross sectional view taken along line III-III shown in FIG. 2;

[0016]FIG. 4 is a cross sectional view taken along line IV-IV shown in FIG. 2;

[0017]FIG. 5 is a side view showing a rubber product M obtained by vulcanization which is an intermediate element of the liquid filled vibration isolator;

[0018]FIG. 6 is a front view showing the rubber product M obtained by vulcanization;

[0019]FIG. 7 is a cross sectional view taken along line VII-VII shown in FIG. 6;

[0020]FIG. 8 is a cross sectional view taken along line VIII-VIII shown in FIG. 5;

[0021]FIG. 9A is a plan view showing a passage forming member;

[0022]FIG. 9B is a front view showing the passage forming member;

[0023]FIG. 9C is a side view showing the passage forming member;

[0024]FIG. 10 is a plan view showing a state of the liquid filled vibration isolator incorporating a passage forming member structured to reciprocate one time in which a portion of the outer cylindrical metal member has been removed;

[0025]FIG. 11 is a plan view showing a state of a liquid filled vibration isolator according to a modification in which a portion of the outer cylindrical metal member has been removed;

[0026]FIG. 12 is a plan view showing a state of a conventional liquid filled vibration isolator in which a portion of an outer cylindrical metal member has been removed:

[0027]FIG. 13 is a cross sectional view taken along line X-X shown in FIG. 12;

[0028]FIG. 14 is a cross sectional view taken along line Y-Y shown in FIG. 13;

[0029]FIG. 15A includes a plan view showing a passage forming member of a conventional liquid filled vibration isolator;

[0030]FIG. 15B includes a front view showing the passage forming member of the conventional liquid filled vibration isolator; and

[0031]FIG. 15C includes a side view showing the passage forming member of the conventional liquid filled vibration isolator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0032] An embodiment of the present invention will now be described with reference to the drawings. FIGS. 1 to 4 are a side view, a partially-broken plan view, a cross sectional view in an axial direction and a cross sectional view in a direction perpendicular to the axial direction each showing a liquid filled vibration isolator according to the embodiment.

[0033] The liquid filled vibration isolator incorporates an inner cylindrical metal member 10 which is a pipe-shape metal member. Moreover, a cylindrical intermediate metal member 20 is coaxially disposed around the inner cylindrical member 10 at a position apart from the inner cylindrical member 10. The intermediate member 20 has paired ring portion 21 and a connection portion 25 for connecting the ring portions 21 to each other. Moreover, a cylindrical rubber member 30 is disposed which integrally connects the intermediate member 20 and the inner cylindrical member 10 to each other. In addition, a passage forming member 40 is disposed which closes the opening of the connection portion 25 and which extends in the circumferential direction. Moreover, an outer cylindrical metal member 50 is provided which is secured to the outside portion of the intermediate member 20 and the passage forming member 40 through a sealing member 51 in a liquid-tight manner. The outer cylindrical member 50 forms an orifice passage K3 in a space from the passage forming member 40 and a main liquid chamber K1 and a sub-liquid-chamber K2 which are allowed to communicate with each other through the orifice passage K3.

[0034] As shown in FIG. 6, each of the ring portions 21 of the intermediate member 20 has a structure that a substantially inner half portion in the axial direction of a substantially half portion (a lower half portion in the drawing) in the circumferential direction is, through an inclined portion 22, formed into a small-diameter portion 23 having a reduced diameter as compared with the outer half portion in the axial direction. As shown in FIG. 2, passage forming recesses 24 are formed in a portion of the ring portions 21 opposite to the small-diameter portion 23 in the radial direction. The passage forming recesses 24 are formed at positions interposing an opening 26 of the connection portion 25 to be described later. The passage forming recess 24 has a shape that a substantially inner half portion in the axial direction is recessed into a trapezoidal shape when it is viewed in a plan view.

[0035] The connection portion 25 for connecting the ring portions 21 to each other has a diameter which is smaller than that of the small-diameter portion 23. An axial directional portion of the connection portion 25 corresponding to the small-diameter portion 23 is, as shown in FIG. 7, recessed into a V-shape portion 25 a having a substantially V-shape cross section in a direction perpendicular to the axis. A rectangular opening 26 when it is viewed in a plan view is formed in the central portion of a portion having a circular-arc cross sectional shape in a direction perpendicular to the axial direction opposite to the V-shape portion 25 a in the radial direction. The axial direction of the opening 26 extends to positions adjacent to the two ends of the connection portion 25. The length of the opening 26 in the circumferential direction is about ⅙ of the length of the circumferential length.

[0036] The rubber member 30 has paired side walls 31 which connect the substantially axial-directional overall surfaces of a portion of the ring portions 21 and the connection portion 25 and the inner cylindrical member 10 to each other, each of the paired side walls 31 having a large thickness. An arm portion 32 extending in the axial direction and arranged to connect the connection portion 25 and the inner cylindrical member 10 to each other is formed between the paired side walls 31, the arm portion 32 being disposed in the intermediate member 20. The arm portion 32 has a V-shape gap portion 32 a which is formed between the inner cylindrical member 10 and the V-shape portion 25 a at a position adjacent to the V-shape portion 25 a, the V-shape gap portion 32 a penetrating in the axial direction and also penetrating the side walls 31. In the connection portion 25, a recess 33 is so formed as to be surrounded by the two side walls 31 and the arm portion 32 and opened opposite to the opening 26.

[0037] The rubber member 30 is integrally molded as a rubber product M made of rubber which is an intermediate product including the inner cylindrical member 10 and the intermediate member 20 as shown in FIGS. 5 to 8 by performing vulcanization in a state in which the inner cylindrical member 10 and the intermediate member 20 are placed in a mold (not shown).

[0038] As shown in FIGS. 2 to 4, a passage forming member 40 extending in the circumferential direction such that the passage forming member 40 closes the opening 26 is joined to the connection portion 25 of the intermediate member 20 provided for the rubber product M made of vulcanized rubber. The passage forming member 40 is made of aluminum. As shown in FIG. 9, the passage forming member 40 incorporates an elongated circular-arc plate 41 having a predetermined width and warped into a semicircular shape. A plurality of (three in FIG. 9) partition walls 42 are provided for the outer surface of the circular-arc plate 41. The partition walls 42 are disposed at substantially the same intervals except for the two axial directional ends. Moreover, the partition walls 42 are stood erect and alternately extend from the two ends in the circumferential direction to the positions adjacent to the other ends in the circumferential direction. Moreover, end walls 43 are stood erect at the two ends of the outer surface of the circular-arc plate 41 in the circumferential direction. Thus, the end walls 43 forms a reciprocative passage groove 44 disposed to reciprocate in the circumferential direction of the circular-arc plate 41 together with the partition walls 42. The circular-arc plate 41 has a first communication opening 45 which is allowed to communicate with the recess 33 at a position adjacent to an end of the reciprocative passage groove 44 and a second communication opening 46 opened in the circumferential direction at a position adjacent to another end of the reciprocative passage groove 44 and allowed to communicate with a gap 36 to be described later. The passage forming member 40 is integrally molded by using aluminum die-cast.

[0039] As shown in FIGS. 2 and 9, the partition walls 42 adjacent to one end of the passage forming member 40 in the widthwise direction has a large-width portion 42 a having substantially the same width as that of the reciprocative passage groove 44. The large-width portion 42 a has an air discharge opening 47 which penetrates the large-width portion 42 a in the radial direction. A rubber stopper 38 in the form of a substantially rectangular thick plate is, by vulcanizing, integrally joined to the central position of the reverse side of the circular-arc plate 41 of the passage forming member 40 in the circumferential direction. The stopper 38 projects into the recess 33 of the rubber member 30. Moreover, a resin stopper member 39 in the form of a thick plate is bonded to the surface of the stopper 38 in the radial direction. The stopper member 39 has substantially the same shape as that of the stopper 38 when it is viewed in a plan view. The cross sectional shape of the stopper member 39 in a direction perpendicular to the axial direction is formed into a substantially circular arc shape.

[0040] A V-shape diaphragm member 35 is secured to the V-shape portion 25 a of the connection portion 25 of the intermediate member 20 in the circumferential direction, as shown in FIGS. 3 and 4. The diaphragm member 35 incorporates a rubber diaphragm membrane 35 a having a small thickness supported by the support portions 35 b at the two ends and the center in the circumferential direction. The diaphragm membrane 35 a is secured to the small-diameter portion 23 by the three support portions 35 b so that a gap 36 is created between the V-shape portion 25 a and the diaphragm membrane 35 a. The outer cylindrical member 50 has an inner surface on which a rubber sealing member 51 having a small thickness is formed by vulcanization.

[0041] The rubber product M which is obtained by vulcanization and to which the passage forming member 40 and the diaphragm member 35 have been joined and the outer cylindrical member 50 are immersed in a liquid chamber filled with the liquid, and the outer cylindrical member 50 is coaxially disposed around the rubber product M obtained by vulcanization. As a result, the inside portions of the recess 33 and the gap 36 are filled with the liquid. Moreover, the outer surface of the outer cylindrical member 50 is subjected to a drawing process. Thus, the outer cylindrical member 50 is secured to the outer surface of the rubber product M obtained by vulcanization. As a result, the liquid filled vibration isolator according to this embodiment can be manufactured. Hence it follows that the opening of the recess 33 of the rubber member 30 is closed in a liquid-tight manner. It leads to a fact that the main liquid chamber K1 is created which is filled with the liquid. Moreover, the sub-liquid-chamber K2 having the gap 36 filled with the liquid is created. The reciprocative passage groove 44 of the passage forming member 40 is filled with the liquid so as to be formed into the orifice passage K3 for allowing the main liquid chamber K1 and the sub-liquid-chamber K2 to communicate with each other.

[0042] Note that the outer cylindrical member 50 is used as a joining metal member as it is. As an alternative to this, a cylindrical joining member is press-fit to the outer surface of the outer cylindrical member 50.

[0043] The passage forming member 40 has the air discharge opening 47 formed in a portion of the partition walls 42 in addition to the first communication opening 45. Therefore, air can be discharged from the two portions which are the first communication opening 45 and the air discharge opening 47 when the liquid is enclosed during the operation for joining the rubber product M obtained by vulcanization and the outer cylindrical member 50 to each other. Therefore, removal of a bubble in the main liquid chamber K1 can easily and reliably be performed. Since the air discharge opening 47 is formed in a portion of the partition walls 42, the passage of the passage forming member 40 is narrowed. However, no partition wall is disposed at each of the two ends of the passage forming member 40 in the widthwise direction, and the passage forming recess 24 is formed at the position opposite to the air discharge opening 47 of the intermediate member 20. Therefore, an appropriate width for the passage can be maintained. It leads to a fact that the passage forming member 40 enables the passage having an appropriate width and a sufficient length to be maintained. Since no partition wall is provided for each of the two ends of the passage forming member 40 in the widthwise direction, the weight and cost of the passage forming member 40 can be reduced.

[0044] As shown in FIG. 9A to 9C, the passage forming member 40 has short-cut preventive walls 48 stood erect at positions adjacent to one end of the circular-arc plate 41 in the circumferential direction and at the two ends of the circular-arc plate 41 in the widthwise direction. The short-cut preventive walls 48 project slightly in the circumferential direction at the two ends. The height of each of the short-cut preventive walls 48 is the same as that of each of the partition walls 42. Since the short-cut preventive walls 48 are stood erect, short-cut between an intermediate position of the orifice passage K3 of the passage forming member 40 and the sub-liquid-chamber K2 can reliably be prevented even if the position joined of the passage forming member 40 is slightly deviated in the circumferential direction. Note that the short-cut preventive walls 48 may be omitted from the structure as necessary.

[0045] The thus-structured liquid filled vibration isolator is disposed such that the inner cylindrical member 10 is connected to, for example, a support member (not shown) of the car body. Moreover, the outer cylindrical member 50 is connected to a support member (not shown) in the engine portion. Moreover, the liquid filled vibration isolator is disposed such that the main liquid chamber K1 and the sub-liquid-chamber K2 are disposed on the upper portion and the lower portion in the vertical direction which is the direction into which main vibrations of the engine are input. If vibrations are produced between the inner cylindrical member 10 and the outer cylindrical member 50, the elastic action of the rubber member 30 and the resonant action of the liquid column of the liquid which flows in the orifice passage K3 damp the vibrations. If an excessively intense vibrations are produced between the inner cylindrical member 10 and the outer cylindrical member 50, the lead end surface of the stopper member 39 is brought into contact with the outer surface of the inner cylindrical member 10. Therefore, displacement can be restrained to satisfy a predetermined range.

[0046] As described above, the liquid filled vibration isolator according to this embodiment has the structure that the passage forming member 40 has the air discharge opening 47. Therefore, the operation for enclosing the liquid can easily be performed. Since an orifice passage having an appropriate width is formed, an appropriate vibration isolating function can be maintained. Moreover, the weight and the manufacturing cost of the passage forming member 40 can be reduced.

[0047] The passage forming member 40 according to this embodiment has the structure that the circular-arc plate 41 is provided with the three partition walls 42 and, therefore, two reciprocative passages are formed. However at least one partition wall may be provided. When the number of the partition walls 42 is made to be one as shown in FIG. 10, one reciprocative passage can be formed. When two partition walls are provided, one and half reciprocative passage can be formed.

[0048] A modification of the passage forming member will now be described.

[0049] As shown in FIG. 11, the modification is structured such that the air discharge openings are formed by providing a projection 65 formed in a reciprocative passage groove 64 of the circular-arc plate 61 except for the partition walls 62. The projection 65 projects outwards in the radial direction in a predetermined region. Moreover, an air discharge opening 66 for penetrating the projection 65 in the radial direction is provided for the projection 65. Also the above-mentioned structure attains the effect of the air discharge openings similar to the foregoing embodiment. As for the width of the passage narrowed by the projection 65, the passage forming recess 24 is provided for the intermediate member 20 at a position opposite to the air discharge opening 66 similarly to the foregoing embodiment. Therefore, an appropriate width of the passage can be maintained. Therefore, also the passage forming member 60 attains an effect similar to that obtainable from the passage forming member 40.

[0050] In the foregoing embodiment, the large-width portion 42 a is provided for the partition walls 42 and the air discharge opening 47 is provided for the large-width portion 42 a. However the large-width portion and the air discharging opening may be omitted. Thus, the weight and cost of the passage forming member can be reduced. Similarly, the projection according to the modification may be omitted.

[0051] Note that the liquid filled vibration isolator according to the embodiment is an example. Therefore, a variety of modification may be permitted within the scope of the present invention. 

1. A liquid filled vibration isolator comprising; an inner cylindrical metal member; a cylindrical intermediate metal member disposed on the outside of said inner cylindrical metal member at a position apart from said inner cylindrical metal member and incorporating paired ring portions formed at two ends in the axial direction, a connection portion for integrally connecting said paired ring portions to each other and an opening formed in a direction in which main vibrations are input; a rubber member constituted by paired side wall portions for connecting said paired ring portions of said intermediate metal member and said inner cylindrical metal member to each other, an arm portion for connecting said paired side wall portions in an axial direction to connect said connection portion and said inner cylindrical metal member, a recess surrounded by said paired side wall portions and said arm portion and opened in said opening, a thin diaphragm portion disposed opposite to said opening in a radial direction such that said thin diaphragm portion is disposed apart from said inner cylindrical metal member and said arm portion at a position between said paired ring portions of said intermediate metal member, and a rubber sealing portion disposed on the outer surface of said cylindrical intermediate metal member; a passage forming member incorporating a circular-arc plate disposed on the outside of said connection portion and extending in the circumferential direction to close said opening, a reciprocative passage groove formed in the outer surface of said circular-arc plate to reciprocate between two ends in the circumferential direction, a first communicate opening allowed to communicate with said recess at one end of said reciprocative passage groove and a second communicate opening opened in the circumferential direction at another end of said reciprocative passage groove; and an outer cylindrical metal member secured to the outside portion of said cylindrical intermediate metal member and said passage forming member, arranged to cause said rubber sealing portion to close a space from said cylindrical intermediate metal member in a liquid-tight manner to form a main liquid chamber in said recess and a sub-liquid-chamber defined by said diaphragm portion and capable of forming an orifice passage in a space from said passage forming member to allow said main liquid chamber and said sub-liquid chamber to communicate with each other, wherein said reciprocative passage groove which is formed into said orifice passage is formed by at least one partition wall extended from either end of said circular-arc plate in the circumferential direction except for the two ends of said circular-arc plate in the widthwise direction and end walls stood erect at two ends of said circular-arc plate in the circumferential direction.
 2. A liquid filled vibration isolator according to claim 1 , wherein an air discharging opening which penetrates said partition wall in the radial direction and allowed to communicate with said recess is provided for a portion of said partition wall.
 3. A liquid filled vibration isolator according to claim 1 , wherein a projection outwards projecting in the radial direction is provided for a portion of said reciprocative passage groove, and an air discharging opening which penetrates said projection in the radial direction and allowed to communicate with said recess is provided for said projection.
 4. A liquid filled vibration isolator according to claim 2 or 3 , wherein a passage forming recess allowed to communicate with said reciprocative passage groove is provided for a portion of said cylindrical intermediate metal member opposite to said air discharging opening in the axial direction. 